In general, a small-sized camera module is mounted in mobile terminals such as a smartphone. In such a camera module, a lens driving device having an auto-focusing function (hereinafter referred to as “AF (Auto Focus) function”) of automatically performing focusing at the time of capturing a subject is applied.
An auto-focusing lens driving device includes an auto-focusing driving part (hereinafter referred to as “AF driving part”) for moving the lens part in the light axis direction. The AF driving part includes, for example, an auto-focusing coil part (hereinafter referred to as “AF coil part”) disposed around the lens part, and an auto-focusing magnet part (hereinafter referred to as “AF magnet part”) disposed separately from the AF coil part in the radial direction. An auto-focusing movable part (hereinafter referred to as “AF movable part”) including the lens part and the AF coil part is moved with respect to an auto-focusing fixing part (hereinafter referred to as “AF fixing part”) including the AF magnet part in the light axis direction by use of a driving force of a voice coil motor composed of the AF coil part and the AF magnet part, and thus focusing is automatically performed.
Conventionally, for example, a method of adjusting the focusing position by analyzing multiple pieces of image information acquired with the image sensor while moving the lens part, and by performing contrast evaluation has been employed. With such a method, however, focusing takes time, and the time period until capturing is long.
In view of this, in recent years, a method (so-called closed loop control system) has been increasingly used in which the lens position is detected at all times with a position detection device mounted in a camera module, and the operation of an AF driving part (voice coil motor) is controlled based on the detection result. The method of detecting the lens position includes methods of detecting the lens position based on variation in magnetic field by use of a Hall device, and methods of detecting the lens position based on variation in light incident on a light reception part by use of an optical sensor (for example, a reflection-type photo reflector) (for example, PTL 1).
A reflection-type photo reflector is an optical sensor in which a light emission part and a light reception part are included in one semiconductor package, light (for example, infrared ray) emitted from the light emission part is reflected by a detection object, and the position of the detection object is detected based on the intensity of reflection light incident on the light reception part. In the case where the position of an AF movable part with respect to an AF fixing part is detected by utilizing the above-mentioned reflection-type photo reflector, it is necessary to mount the reflection-type photo reflector in the AF fixing part, and dispose a reflection plate (for example, an aluminum mirror) in the AF movable part.